Micromirror Array Assembly with In-Array Pillars

ABSTRACT

The present invention provides a microstructure device comprising multiple substrates with the components of the device formed on the substrates. In order to maintain uniformity of the gap between the substrates, a plurality of pillars is provided and distributed in the gap so as to prevent decrease of the gap size. The increase of the gap size can be prevented by bonding the pillars to the components of the microstructure. Alternatively, the increase of the gap size can be prevented by maintaining the pressure inside the gap below the pressure under which the microstructure will be in operation. Electrical contact of the substrates on which the micromirrors and electrodes are formed can be made through many ways, such as electrical contact areas, electrical contact pads and electrical contact springs.

TECHNICAL FIELD OF THE INVENTION

The present invention is related generally to the art ofmicroelectromechanical systems, and, more particularly, to spatial lightmodulators having array of micromirrors and methods of making the same.

BACKGROUND OF THE INVENTION

Microstructures such as microelectromechanical systems are oftenfabricated on one or more substrates. These substrates may deform duringfabrication or operation, causing degradation of the device performanceor even device failure when the deformation exceeds a tolerable amount.Moreover, in those microstructures having multiple substrates, a uniformgap between two substrates is often required for ensuring desiredfunctions or performance of the microstructure.

As an example, FIG. 1 illustrates a portion of a micromirror arraydevice which is a type of microelectromechanical device. An array ofmirror plates such as mirror plate 120 is formed on glass substrate 116.The mirrors are operable to rotate relative to the glass substrate forreflecting light into different directions. The micromirrors areindividually addressable and the addressing can be accomplished throughan array of electrodes (e.g. electrode 122) and circuitry onsemiconductor substrate 114. Specifically, an electrostatic field isestablished between each mirror plate and the electrode associated withthe mirror plate. The strength of such electrostatic field complies withthe voltage (often referred to as data bit) stored in the circuitryconnected to the electrode. By setting the voltage through writing thedata bit in the circuitry, the strength of the electrostatic field andthus the rotation position of the mirror plate can be adjusted. Becausethe rotation of the mirror plate is determined by the strength of theelectrostatic field that further depends upon the distance between themirror plate and the associated electrode, it is desired that suchdistance is uniform for all micromirrors.

However, a uniform distance throughout the micromirror array may not beguaranteed in fabrication or in operation or in both due to deformationof the substrates on which the micromirrors and electrodes are formed.The deformation may arise from many factors, such as temperature change,variation of the pressure applied to the substrates and other factors,such as attractive or expellant electrostatic forces between thesubstrates when the substrates are electrically charged. The deformationchanges the gap size, which in turn changes the effective strength ofthe electrostatic field. As a consequence, desired operation orperformance of the device is not achievable.

In addition to the substrate deformation, other factors, such asoperation environment (e.g. contamination and viscosity) may alsodegrade the operation and performance of the micromirror array device.Contamination is often solved by packaging the device, such ashermetically packaging the device. Viscosity problems arise from theviscosity resistance to the rotation of the mirror plate in a medium,such as air or the gas (e.g. an inert gas). The viscosity resistance tothe movement of the mirror plate reduces the response time of the mirrorplate and limits the application of the micromirror array device.

Therefore, what is needed is a micromirror array device that ismechanically robust and has improved performance.

SUMMARY OF THE INVENTION

In an embodiment of the invention, a microelectromechanical (MEMS)device is disclosed. The device comprises: a first substrate and asecond substrate; a plurality of MEMS elements formed on the firstsubstrates; and a plurality of pillars disposed between the secondsubstrate and the MEMS elements.

In another embodiment of the invention, a spatial light modulator foruse in a projection system is disclosed. The spatial light modulatorcomprises: a micromirror array device, comprising: a first substratehaving thereon an array of micromirrors; a second substrate having anarray of electrodes for deforming the micromirrors; and a plurality ofpillars disposed between the substrates such that the first substrate isconnected to the second substrate via the micromirror and the pillar formaintaining a uniform gap between the substrates.

In yet another embodiment of the invention, a micromirror device isdisclosed. The device comprises: a first substrate; a post on thesubstrate; a mirror plate attached to a hinge that is held by the poston the substrate such that the mirror plate rotates on the substrate; apillar on the mirror plate and in connection with the post; and a secondsubstrate having an electrode and circuitry disposed thereon forrotating the mirror plate, wherein the second substrate is disposed onthe pillar and connected to the pillar such that the distance betweenthe first and second substrate is maintained at a substantially constantvalue.

In yet another embodiment of the invention, a method of making a spatiallight modulator is disclosed. The method comprises: forming an array ofmicromirrors on first substrate; forming an array of electrodes andcircuitry on second substrate; forming a plurality of pillars on thesecond substrate; aligning each pillar with one of the micromirrors; andbonding the substrates.

In yet another embodiment of the invention, a micromirror array deviceis disclosed, which comprises: a substrate having thereon an array ofmicromirrors, further comprising: at least two electrical contact pads,each of which is electrically connected to the micromirrors such that amelectrical resistance of the micromirrors of the array can be measuredthrough the electrical contact pads; and an array of electrodesassociated with the micromirrors for deflecting the micromirrors.

In yet another embodiment of the invention, a spatial light modulator isprovided, which comprises: an array of micromirrors on a firstsubstrate; an array of electrodes and circuitry on a second substrate; afirst sealing material that hermetically bonds the first and secondsubstrates; and a second sealing material other than the first sealmaterial contracting the first and second substrate for enhancing thehermetic seal with the first sealing material.

In yet another embodiment of the invention, a microelectromechanicaldevice is provided. The device comprises: a first and second substratebonded together; an array of MEMS elements formed on the first substrateand disposed between the substrates; an array of electrodes andcircuitry disposed between the bonded substrates but spaced apart fromthe array of MEMS elements; and a plurality of pillars disposed betweenthe second substrate and the MEMS elements.

In yet another embodiment of the invention, a method of forming aspatial light modulator for use in a display system is disclosed. Themethod comprises: forming a plurality of micromirrors on a lighttransmissive substrate, wherein each micromirror has a fixed portion anda movable portion; forming a plurality of electrodes and circuitry on asemiconductor substrate; and forming a pillar on the fixed portion ofthe micromirror and/or on the semiconductor substrate.

BRIEF DESCRIPTION OF DRAWINGS

While the appended claims set forth the features of the presentinvention with particularity, the invention, together with its objectsand advantages, may be best understood from the following detaileddescription taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a cross-sectional view of a portion of the spatial lightmodulator in prior art;

FIG. 2 illustrates a display system having a spatial light modulator inwhich embodiments of the invention can be implemented;

FIG. 3 is a perspective view of a portion of a spatial light modulatorhaving an array of micromirrors according to the invention;

FIG. 4 is a perspective view of a portion of a micromirror of themicromirror array in FIG. 3;

FIG. 5 through FIG. 10 are cross-sectional views of micromirror devicesaccording to different embodiments of the invention;

FIG. 11 is a cross-sectional view of a spatial light modulator inaccordance with an embodiment of the invention;

FIG. 12 is a cross-sectional view of a spatial light modulator inaccordance with another embodiment of the invention;

FIG. 13 is a top view of a micromirror array device formed on a die;

FIG. 14 plots a distribution of the pillars density and distribution ofsubstrate distortion of the micromirror array deice on the die in FIG.13;

FIG. 15 through FIG. 18 illustrate an exemplary fabrication process ofmicromirror array device in FIG. 13;

FIG. 19 is a cross-sectional view of the micromirror device on a packagesubstrate according to an embodiment of the invention;

FIG. 20 is a another cross-sectional view of the micromirror device ofFIG. 19;

FIG. 21 is a top view of the micromirror array device assembly of FIG.19;

FIG. 22 is a top view of another the micromirror array device assembly;

FIG. 23 is a cross-sectional view of a micromirror array device assemblyaccording to another embodiment of the invention;

FIG. 24 is a perspective view of a micromirror device during afabrication according to an embodiment of the invention;

FIG. 25 is a cross-sectional view of a plurality of micromirror devicesduring an exemplary fabrication according to the invention; and

FIGS. 26A and 26B are cross-sectional views of a micromirror device inFIG. 25 before and after removal of a substrate provided during thefabrication for protecting the surface of the micromirror device.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention provides a microstructure device comprisingmultiple substrates with the functional components of the device formedon the substrates. In order to maintain a uniform gap between thesubstrates, a plurality of pillars is provided and distributed withinthe gap. The gap uniformity can further be enhanced by maintaining thepressure inside the gap below the pressure under which themicrostructure device will be in operation.

In the following, the present invention will be discussed with referenceto examples in which a microelectromechanical device comprises an arrayof micromirrors formed on two substrates. It is understood by thoseskilled in the art that the following discussion is for demonstrationpurposes only and will not be interpreted as a limitation. Though theinvention will be discussed with reference to the following example, itis not intended to exclude other variations within the scope of thepresent invention. For example, the present invention can be implementedin other microstructures having functional components formed on singleor multiple substrates.

Turning to the drawings, FIG. 2 illustrates an exemplary display systemin which embodiment of the invention may be implemented. In its basicconfiguration, display system 100 comprises light source 102, opticalelements (e.g. light pipe 104, collection lens 106 and projection lens108), display target 112 and spatial light modulator 110 that oftencomprises an array of thousands or millions of micromirrors that areindividually addressable.

In operation, light from the light source (e.g. an arc lamp) travelsthrough the light pipe and collection lens and shines on themicromirrors of the spatial light modulator. The micromirrorsindividually reflect the incident light from the light source eitheronto (when in their “ON” position) or away from (when in their “OFF”state) the projection lens, resulting in an image on display target 112.

FIG. 3 shows a portion of an exemplary spatial light modulator in FIG.2. The spatial light modulator comprises an array of mirror plates 124formed on glass substrate 116, which is transmissive to visible light.The mirror plates are individually addressable and operable to rotatefor reflecting incident light from the light source into differentspatial directions. The rotation of the mirror plates is driven by anarray of electrodes (e.g. electrode array 126) formed on substrate 114,which is a semiconductor substrate further having an array of circuitry(not show in the figure). The gap between the glass and semiconductorsubstrates is defined and maintained by one or more pillars, such as128, which is better illustrated in FIG. 4. The distribution of thepillars in the micromirrors can be random or in accordance with aparticular pattern, which will be discussed afterwards with reference toFIG. 15 through FIG. 18.

Referring to FIG. 4, two posts 134 are formed on the glass substrate116. The posts can be placed at any desired position relative to themirror plate. For example, the posts can be placed at the ends of apredominant diagonal of the mirror plate such that a line connecting theposts is parallel to the diagonal. For another example, the posts can beplaced around the ends of a predominant diagonal. For yet anotherexample, the posts can be placed on the sides of the mirror plate. Otherarrangements of the posts are also applicable. Hinge 136 is held by theposts on the substrate. The mirror plate is attached to the hinge suchthat the mirror plate can rotate above the glass substrate. As beingillustrated in the figure, the mirror plate is attached to the hingesuch the mirror plate can rotate asymmetrically. That is, the mirrorplate can rotate to a larger angle in one direction than in the oppositedirection. The hinge is parallel to but offset from a diagonal of themirror plate when viewed from the top, and the attachment point of themirror plate to the hinge is neither at the center of the mirror platenor along a virtual line connecting posts 130A and 130B. In otherexamples, the mirror plate and the hinge can be formed such that themirror plate can rotate symmetrically. Moreover, the hinge may notnecessarily be a torsion hinge as shown in the figure. Instead, thehinge can be another type of non-torsion hinges (e.g. flexure hinge).The mirror plate rotates in response to an electrostatic fieldestablished between the mirror plate and the electrode that is formed onthe semiconductor substrate, which is not shown in this figure. In orderto keep a uniform gap between the substrates, pillars 128 are providedand the pillars are located on top of the posts and between the postsand the semiconductor substrate (not shown).

The pillars may take any desired form, such as polyhedron or cylinder.In this particular example, the pillars are tapered polyhedron with thebutt ends contacting against the semiconductor substrate and the tailends contacting against the posts (this shape due to being formed on thesemiconductor substrate). The figure shows the micromirror has two postsand two pillars contacting the posts, this is not an absoluterequirement. The micromirror may comprise two posts while only onepillar is provided for the micromirror. As another example, themicromirror may have only one post with one pillar connected to the postof the micromirror. In a micromirror array device such as that shown inFIG. 3, a pillar may not be provided for all micromirrors of the array,which will be discussed further afterwards with reference to FIG. 13 andFIG. 14.

The relative position of the posts, the pillars, and the substrates isbetter illustrated in FIG. 5, which is a cross-sectional view of themicromirror in FIG. 4 along line AA. Posts 134A and 134B are formed onglass substrate 116. Hinge 133 is held on the glass substrate by theposts. Mirror plate 132 is attached to the hinge such that the mirrorplate can rotate relative to the substrate. Pillars 130A and 130B areformed on semiconductor substrate 114 that further comprises anelectrode and circuitry for rotating the mirror plate (not shown). Eachpillar is connected to a post such that the size of the gap between thesubstrates is defined as the summation of the heights of the post andthe pillar and maintained at this constant value during operation. Thepillar can be of any desired height. In this example, the height of thepillar is substantially equal to or greater than the height of the post.The contact point of the post to the pillar is substantially in themiddle of the gap. In another example, the pillar is shorter than thepost. As a result, the contact point of the pillar to the post is closerto substrate 114 than to substrate 116. In yet another example, thepillar has a larger height than the post. In this situation, the contactarea of the post to the pillar is closer to substrate 116 than tosubstrate 114.

Instead of providing pillars for both posts of the micromirror device,the micromirror may have only one pillar as shown in FIG. 6. The pillaris connected to one of the posts of the micromirror device.

The pillar may comprise any suitable materials, such as polyimide orSU-8. SU-8 is a negative, epoxy-type, near-UV photoresist based on EPONSU-8 epoxy resin that has been originally developed, and patented (U.S.Pat. No. 4,882,245). As another example, the pillar comprises a materialthat has a coefficient of thermal expansion (CET) matching the CTE ofthe post. The pillar may alternatively comprise a material with a highthermal conductivity for improving heat dissipation. The material of thepillar can be electric conducting or insulating.

FIG. 7 shows another exemplary micromirror device with pillars provided.Instead of being connected to the posts, the pillars are connected tothe protrusions of the posts. Specifically, pillar 130A is formed onsubstrate 114 and connected to protrusion 135A that is formed on post134A, and pillar 130B is likewise formed on substrate 114 and connectedto protrusion of 135B that is formed on post 134B. The protrusions mayor may not be the same. The pillars of the microstructure also may ormay not be the same. FIG. 8 shows the micromirror of FIG. 7 with onlyone pillar provided.

Referring to FIG. 9, a cross-sectional view of a micromirror deviceaccording to yet another embodiment of the invention is illustratedtherein. In this particular example, pillars 135A and 135B are formed onthe posts of the micromirror device and connected to substrate 114 whenthe two substrates are bonded together. Specifically, pillar 135A isformed on post 134A and connects post 134A to substrate 114. Likewise,pillar 135B is formed on post 134B and connects post 134B to substrate114. The lengths of a post and the pillar formed on the post determinethe gap between the two bonded substrates. The pillars and the posts incombination resist variation of the gap between the two substrates. Asan alternative, not all posts of the micromirror device are providedwith pillars. As an example shown in FIG. 10, one of the posts of themicromirror device is not provided with a pillar, however, at least onepost of the micromirror device is provided with a pillar. In otheralternatives wherein the micromirror device is part of a micromirrorarray device, a particular micromirror device of the array may not havea pillar, which will be discussed in the following with reference toFIGS. 13 and 14.

In a device having an array of micromirrors, pillars may be provided forselected micromirrors. Referring to FIG. 11, a cross-sectional view of arow of the micromirror array from a different view angle from FIGS. 5 to10 is illustrated therein. For simplicity purposes only, only threemicromirrors are shown. The cross-section is taken along the lineconnecting the posts of the micromirror. In this particular example,micromirror 148 is provided with pillars (e.g. pillars 140A and 140B),while micromirrors 150 and 152 in the row of the array have no pillars.The pillars of micromirror 148 can be the pillars as discussed withreference to FIGS. 5 through 10, or any desired pillars that are notdiscussed herein but are variations of the pillars as discussed above.

FIG. 12 illustrates another exemplary micromirror array device. In thisexample, pillars are provided for micromirrors 154, 156 and 158. Themicromirrors (with the number of n, wherein n is an integer and zero)between micromirrors 154 and 156 are not provided with pillars. And themicromirrors (with the number of m, wherein m is an integer and zero andmay or may not be the same as n) between micromirrors 156 and 158 arenot provided with pillars.

FIG. 13 illustrates a top view of the micromirror array device, such asthe device in FIG. 1. The solid circles represent micromirrors eachhaving at least one pillar. The open circles represent micromirrorshaving no pillar. In this example, pillars are provided for thosemicromirrors around the center of the device. This arrangement is incompliance with an observation that the substrate (e.g. substrate 116 inFIG. 1) has more deformation around the center and less near the edge.An exemplary distribution of the substrate deformation is illustrated asthe dotted line in FIG. 14. Rather than providing the pillars only forthe micromirrors near the center, the provided pillars may bedistributed in the micromirrors as desired. For example, in addition toproviding the pillars to the micromirrors around the center of themicromirror array device, pillars are also provided for selectedmicromirrors not around the center of the micromirror array device. Thedashed line in FIG. 14 plots the density (defined as the number ofpillars per unit area) of the pillars distributed in the micromirrors ofan exemplary micromirror array device. The micromirrors in a region(having number of P micromirrors) around the center of the array areprovided with at least one pillar. For the remaining micromirrors, thepillars are provided according to the distance from the edge of thedevice, wherein the distance is measured by the number of micromirrors.Specifically, the density of the pillars in those micromirrors can belinear. In an example, a plurality of pillars is provided for themicromirror array device and is randomly distributed in the micromirrorsof the array.

The micromirror array and the micromirror having a pillar can befabricated in many ways. In the following, an exemplary fabricationmethod will be discussed with reference to FIG. 15 through FIG. 18. Itis understood by those skilled in the art that the method is applicableto other micromirror array devices having different pillar distributionsor other type of microstructures having pillars between substrates.

Referring to FIG. 15, an array of mirror plates is formed on glasssubstrate 116. Specifically, first sacrificial layer 164 is deposited onthe glass substrate followed by deposition of the mirror plate layer160. The glass substrate may have other films deposited thereon. Forexample, optical coating films, such as anti-reflection films 160 and162 can be deposited on each surface of the glass substrate. Othercoating films may also be deposited on the surfaces of the glasssubstrate or on the deposited optical films before depositing the firstsacrificial layer. The mirror plate layer is then patterned into desiredshapes. Second sacrificial layer 166 is deposited on the patternedmirror plates for forming the hinge (not shown) and posts (e.g. posts142A and 142B). After the hinge and the posts are formed, thesacrificial layers are removed using selected etchant, such as a vaporphase interhalogen (e.g. bromine fluorides) and noble has halide (e.g.xenon fluorides). The micromirror array device after removing of thesacrificial layers is illustrated in FIG. 16.

The method as discussed above is applied to fabricate a micromirror withthe hinge and the mirror plate on separate planes. This method is alsoapplicable to fabricate a micromirror as shown in FIG. 7 or alike, inwhich post protrusions are provided. To obtain such a micromirror, athird sacrificial layer may be deposited on the second sacrificiallayer. The posts protrusions are then formed on the third sacrificiallayer.

After removal of the sacrificial layers, other structures can be formed.For example, a getter (e.g. a non-evaporate getter or dispensablegetter) can be provided in trench 174A for absorbing containments, suchas moisture or particles. The trench can be formed at any desiredlocation of the substrate, such as a location near the edge of thesubstrate as shown in the figure.

In another example, light absorbing layer 170 can be formed on layer 164that is deposited on substrate 116. Layer 164 can be the first or thesecond sacrificial layer. The light absorbing layer 170 can be ametallic layer that absorbs light from the light source so as to reducelight scattering and absorb scattered light by the components of themicromirrors or incoming light. On the metallic layer 170, ametallization bonding layer 172A can be deposited for bonding the glasssubstrate to the semiconductor substrate 114 in FIG. 1. In this example,the layers 164, 170 and 172 surround the circumference of the substrate116.

The fabrication of the pillars on the semiconductor substrate isillustrated in FIG. 17. Referring to FIG. 17, the semiconductorsubstrate 114 comprises an array of circuitry (e.g. DRAM or other typeof memories) that is not shown. Layer 176 is deposited on the surface ofthe substrate for passivating the surface. The pillars 140A and 140B canbe formed on the electrode by many ways, such as spinning the pillarmaterial, curing the spun pillar material and patterning the curedpillar material on the electrode into desired shapes. As an example, thepillar is a tapered polyhedron. In addition to the pillars, otherstructures may be formed on substrate 114. For example, layer 180comprising the pillar material can be formed and patterned followed bydeposition and patterning of metallization layer 172B. Layers 180 and172 fully surround the circumference of the substrate 114. layer 180 andpillars 140A and 140B may have the same material, though not required.Trench 174B can be formed for holding a getter (e.g. a non-evaporategetter or dispensable getter) material so as to absorb containments,such as moisture or particles. The trench can be formed at any desiredlocation of the substrate, such as a location near the edge of thesubstrate.

The glass (or quartz) substrate 116 with micromirrors formed thereon asshown in FIG. 17 and the semiconductor (e.g. silicon) substrate 114 withthe electrodes and pillars formed thereon as shown in FIG. 16 are thenbonded together as shown in FIG. 18. Referring to FIG. 18, substrates114 and 116 are first aligned such that the pillars are aligned with thecorresponding posts. Meanwhile, sealing ring 182 comprising layers 164,170 and 172 on substrate 116 are aligned with the sealing ringcomprising layers 180 and 172 on substrate 114. The aligned substratesand the sealing rings on the substrates are cured. As an example, thesubstrates and the sealing rings are cured at a temperature of from 100°C. to 200° C., or around 120° C. As another example, the substrates canbe cured at the melting temperature or higher of the metallizationlayers 172. The metallization layers 172 on the substrates 114 and 116are then melted to bond the substrates and form a hermetic seal to thesubstrates. The bonded and hermetically sealed substrates are thencooled down to a temperature below 100° C., such as 70° C. As a result,the pressure inside the hermetically sealed space between the substratesis below the atmosphere, such as 500 Torr or lower, or 200 Torr orlower, or 100 Torr or lower. The reduced pressure between the bonded andhermetically sealed substrates is of great importance when themicromirror array device is operated in a typical operation environmentof room temperature and at 1 atmosphere. Specifically, the reducedpressure between the substrates can prevent increase of the gap betweenthe substrates due to outwards expansion of the substrates in thepresence of temperature variation. For this reason, the pressure insidethe hermetically sealed package can be of any pressure below oneatmosphere, such as 250 Torr or less, or 50 Torr or less, or 10 Torr orless, or 1 Torr or less, or 100 mTorr or less. The low pressure insidethe hermetically sealed package can also be obtained through many otherways, such as sealing the package within a low pressure chamber.

As another example, before aligning the substrates, a ultra-violet light(UV) or UV/infra-radiation light curable material, such as epoxy 183 oralike can be deposited around the perimeter of one or both substratesoutside or inside seal ring 182. The substrates are then aligned; and ahermetical seal is formed to bond the substrates. The hermeticallysealed substrates may be cooled down to a temperature below 100° C. toobtain a reduced pressure between the substrates. Epoxy 183 is thencured to add bonding strength to the hermetic seal. Getter materials(e.g. non-evaporate or dispensable getter materials) can be provided intrenches 174A and 174B on the substrates for absorbing containments,such as moisture or particles. The getter materials in the trenches mayor may not be the same. The trench can be formed at any desired locationof the substrate, such as a location near the edge of the substrate.Lubricant materials for lubricating the surfaces of the micromirrordevice can also be disposed in the trenches.

In accordance with an embodiment of the invention, the bonding andsealing of the substrate can be performed in a pressured chamber. Duringthe bonding and sealing, the volume between the two substratesdecreases, resulting in increase of pressure between the substrates.This pressure variation may burst the sealing material between thesubstrates. For this and other reasons, the bonding and sealing of thesubstrates are performed within a chamber that has a pressure proximateto the internal pressure of the seal gap between the substrates. In thisway, the pressure between the substrates during the bonding and sealingis in equilibrium with the environment pressure.

The bonded and hermetically sealed substrates, referred to as anassembly, are packaged, which is shown in FIG. 19. As an example, theassembly comprising bonded substrates 114 and 116 is attached to packagesubstrate 188. Sealing ring 182 is deposited around the perimeter of thesubstrates. A substrate insert 186 can be disposed between substrate 188and substrate 114 for many advantages, such as preventing deformation ofsubstrate 188 and providing efficient heat conductor for dissipatingheat in the assembly.

Electric contact between the micromirrors in substrate 116 andelectrodes on substrate 114 can be made in a variety of ways. As a wayof example, multiple electric contact pads can be provided for themicromirrors in substrate 116, such as two electric contact pads 190Aand 190B in FIG. 21. Referring to FIG. 21, sealing ring comprisesmultiple segments, such as 183A and 183B so as to form gaps between thesegments for allowing the electrical contact pads to pass through. Theelectrical contact pads are connected to the micromirrors of micromirrorarray 124. The multiple electrical contact pads also enable theresistance measurement of the micromirrors of the array. The measuredresistance can be used to determine the quality of the electricalinter-connection of the micromirrors in the array. The electricalcontact pads are then connected to multiple shims 184A and 184B as shownin FIG. 19. Referring back to FIG. 19, shims 184A and 184B extend theelectrical contact pads 190A and 190B onto package substrate 188.Electrical contact wires 196A and 196B are respectively connected to theshims, which is better illustrated in FIG. 20. Referring to FIG. 20,shim 184A electrically contacts electrical contact pad 190A on substrate116 and wire 196A on package substrate 188. And shim 184B electricallycontacts electrical contact pad 190B on substrate 116 and wire 196B onpackage substrate 188. External power supplies can thus be connected tothe wires so as to provide electrical power to the micromirrors.Referring back to FIG. 19, electrical contact of the electrodes (andcircuitry) on substrate 114 can be made through electrical wires 198.The external power supplies can be connected to wire 198 and provideelectrical power to the electrodes. In the above example, two electricalcontact pads are provided for the substrate on which the micromirrorsare formed. In fact, other number (e.g. one, or more than two) ofelectrical contact pads may be formed on substrate 116. Accordingly, thenumber of shims connected to the electrical contact pads changes withthe number of electrical contact pads.

As another example of the invention, electrical contact between the twosubstrates is made through multiple contact areas, such as that shown inFIG. 22. Referring to FIG. 22, multiple contact areas, such as 192A and192B that are connected to the micromirrors of the micromirror array areformed on substrate 116. The contact areas can be of any desired shapesand areas. The areas may also be in different configuration. Forexample, one contact area is rectangular and the other one is circle.The areas can be disposed at any desired locations on the substrate aslong as they are electrically connected to the micromirrors.

Corresponding to contact areas 192A and 192B on substrate 116, contactareas 194A and 194B are formed on substrate 114. When the two substratesare joined together, the electrical contact areas 192A and 194A, and192B and 194B are overlapped so as to form electrical connection.

The electric contacts, such as the electrical contact pads 190A and190B, and electrical contact areas 192A, 912B, 194A, and 194B maycomprise any suitable material, such as electrical conductor (e.g.electrical conducting epoxy) or electrical insulator (e.g.non-electrical-conducting epoxy). When an electrical insulator is used,an electrical conducting spacer (not shown) is provided between thesubstrates (e.g. substrates 114 and 166).

In yet another example of the invention, electrical contact of the twosubstrates are made through a contact spring or alike, as shown in FIG.23. Electrical springs 200 are formed on substrate 188. When the twosubstrates are jointed together, the electrical springs are pressedagainst the electrical contact pads on substrate 116 so as to formelectrical contact. Alternatively, an electrical contacting cantilever202 can be made on substrate 188 for electrically contacting substrate116.

During the assembling and packaging processes, surfaces of themicromirror device may be contaminated. Contamination of the interiorsurfaces of the assembly (e.g. the bottom surface of substrate 116 andthe surfaces of the micromirrors and the top surface of substrate 114)can be prevented by hermetically sealing of substrates 114 and 116 withsealing material 182. However, the exterior surface of the assembly,such as the top surface of the glass substrate 116 is exposed tocontamination. To solve this problem, a sacrificial substrate isprovided and sealed with substrate 116 such that the top surface ofsubstrate 116 can be encapsulated between the sacrificial substrate andsubstrate 116 during the assembly and packaging process, as illustratedin FIG. 24.

Referring to FIG. 24, substrate 114 having the electrode array formedthereon can be hermetically sealed with substrate 116 on which themicromirror array is formed. The hermetical seal is made through sealingmaterial 182. The top surface of substrate 114 and the bottom surface ofsubstrate 116 can thus be prevented from contamination. To protect thetop surface of substrate 116, sacrificial substrate 206 is provided andbonded to substrate 116 with sealing material 208. The sealing ofsubstrates 206 and 116 can be performed before or after the hermeticallysealing of substrates 114 and 116, or during the fabrication process,which will be discussed in detail in the following.

Referring to FIG. 25, a cross-sectional view of a plurality ofmicromirror array devices during fabrication is illustrated therein. Forsimplicity and demonstration purposes only, only four micromirror arraydevices are shown. In an exemplary fabrication process, fabrication ofthe electrode arrays on the standard semiconductor substrate 114 and thefabrication of the micromirror arrays on substrate 116 are performedseparately. For example, the electrode arrays, as well as the associatedcircuitries (e.g. random-access-memories), are formed on substrate 114using standard integrated circuit fabrication techniques. Separate fromthe fabrication of the electrodes, the micromirrors are formed onsubstrate 116. The micromirrors can be fabricated on substrate 116 in averity of ways, such as the methods set forth in U.S. patent applicationSer. No. 10/366,296 to Patel et al, filed on Feb. 12, 2003, Ser. No.10/366,297 to Patel et al, filed on Feb. 12, 2003, Ser. No. 10/402,789to Patel, filed on Mar. 28, 2003, Ser. No. 10/402,889 to Patel, filed onMar. 28, 2003, Ser. No. 10/627,105, filed on Jul. 24, 2003, Ser. No.10/613,379, filed on Jul. 3, 2003, Ser. No. 10/437,776, field on May 13,2003, Ser. No. 10/698,513, filed on Oct. 30, 2003, the subject matter ofeach being incorporated herein by reference. During the fabrication ofthe micromirrors on substrate 116, sealing rings, such as sealing ring208 is deposited on the top surface of substrate 116. An exemplarysealing ring 208 is illustrated in FIG. 24. Sacrificial substrate 206,which can be glass, is bonded to substrate 116 with the sealing rings208. The sealing rings 208 can also be deposited on sacrificialsubstrate 206. The sealing of the sacrificial substrate 206 andsubstrate 116 can be performed before the fabrication of themicromirrors, for example before depositing a sacrificial layer onsubstrate 116. Alternatively, the sealing of the sacrificial substrateand substrate 116 is made after the formation of the functionalcomponents of the micromirrors but before removing the sacrificialmaterial through etching. In another example, the sealing of thesacrificial substrate and substrate 116 can be made after the removal ofthe sacrificial material but before assembling substrates 114 and 116.

When the micromirror arrays on substrate 116 and the electrode arrays onsubstrate 114 are formed, substrates 114 and 116 are sealed usingsealing material 182. Then the assembly is cut into dies, each diecomprising a micromirror array device, such as the micromirror arraydevice shown in FIG. 3. As an exemplary cutting method of the invention,the sacrificial substrate 206 and substrate 116 are cut along cuttinglines 212A, 212B and 212C as shown in the figure. These cutting linesstop before the bottom surface of substrate 116. Substrate 114 is cutinto segments along cutting lines 210A, 210B and 210C, each of which isoffset from the corresponding cutting lines for substrates 206 and 116.For example, cutting line 210A stops before the top surface of substrate114 and has an offset from cutting line 212A. Cutting line 210B stopsbefore the top surface of substrate 114 and has an offset from cuttingline 212B. After such cutting, micromirror array devices are singulated,such as micromirror array device 218 in FIG. 26A. After the singulation,the sacrificial substrate 206 on each micromirror array device isremoved. The micromirror device 218 in FIG. 26A after removal of thesacrificial substrate 206 is illustrated in FIG. 26B. Sealing material208 on the top surface of substrate 116 may or may not be removed.Instead of removing the sacrificial substrate (206) after singulation,the sacrificial substrate can be removed at other stages during thefabrication. For example, the sacrificial substrate can be removedbefore or during or even after the device testing in which the productquality and performances are evaluated. The removal of the sacrificialsubstrate can also be carried out before or during packaging themicromirror array device but before encapsulating the device with theattachment of the a package cover lid.

It will be appreciated by those of skill in the art that a new anduseful micromirror array device having a plurality of in-array pillarshas been described herein. In view of many possible embodiments to whichthe principles of this invention may be applied, however, it should berecognized that the embodiments described herein with respect to thedrawing figures are meant to be illustrative only and should not betaken as limiting the scope of invention. For example, those of skill inthe art will recognize that the illustrated embodiments can be modifiedin arrangement and detail without departing from the spirit of theinvention. Therefore, the invention as described herein contemplates allsuch embodiments as may come within the scope of the following claimsand equivalents thereof.

1-32. (canceled)
 33. A spatial light modulator for use in a projectionsystem, comprising: a micromirror array device, comprising: a firstsubstrate having thereon an array of micromirrors; a second substrate;and a plurality of pillars disposed between the substrates such that thefirst substrate is connected to the second substrate via the micromirrorand the pillar for maintaining a uniform gap between the substrates. 34.The spatial light modulator of claim 33, further comprising: a sealingmaterial disposed between the substrates for bonding the substrates. 35.The spatial light modulator of claim 34, wherein the bonded substrateand the sealing material therebetween form a hermetically sealed space.36. The spatial light modulator of claim 35, wherein the hermeticallysealed space has a pressure lower than 1 atmosphere.
 37. The spatiallight modulator of claim 33, wherein the micromirror further comprising:a post on the first substrate; a hinge held by the post on the firstsubstrate; and a reflective mirror plate attached to the hinge such thatthe mirror plate is operable to rotate on the first substrate.
 38. Thespatial light modulator of claim 37, wherein the pillar is connected tothe post of the micromirror.
 39. The spatial light modulator of claim38, wherein each micromirror has two posts on the substrate, each postbeing connected to a pillar.
 40. The spatial light modulator of claim33, wherein the pillars is distributed within an area between thesubstrates according to a distribution of deformation in the firstsubstrate under a pressure.
 41. The spatial light modulator of claim 38,wherein the contact point of the pillar to the post is in the same planeas the hinge.
 42. The spatial light modulator of claim 38, wherein thecontact point of the pillar to the post is not in the same plane as thehinge.
 43. The spatial light modulator of claim 38, wherein the mirrorplate, the hinge and the contact point of the pillar to the hinge are onthe same plane.
 44. The spatial light modulator of claim 38, wherein thepillar has a first component that is connected to the post of themicromirror and a second component that is connected to the firstcomponent of the pillar and the second substrate.
 45. The spatial lightmodulator of claim 33, wherein the pillar comprises a material that hasa coefficient of thermal expansion matches that of the material of thepost.
 46. The spatial light modulator of claim 33, wherein the pillarcomprises a material that has a thermal conductivity equal to or lessthan that of the post.
 47. The spatial light modulator of claim 33,further comprising: an optical coating film on a surface of thesubstrate on which the micromirrors are disposed.
 48. The spatial lightmodulator of claim 33, further comprising: a getter material disposed onone of the two substrates for absorbing contaminants.
 49. The spatiallight modulator of claim 33, wherein the sealing material furthercomprises: a first metallization material disposed on a sacrificialmaterial that is disposed on the substrate on which the micromirrors areformed.
 50. The spatial light modulator of claim 34, wherein the sealingmaterial further comprises: a second metallization material disposed ona layer composed of the material of the pillar, wherein said layer andthe second metallization material are disposed on the second substrate.51. A micromirror device, comprising: a first substrate; a post on thesubstrate; a mirror plate attached to a hinge that is held by the poston the substrate such that the mirror plate rotates on the substrate; apillar on the mirror plate and in connection with the post; and a secondsubstrate, wherein the second substrate is disposed on the pillar andconnected to the pillar such that the distance between the first andsecond substrate is maintained at a substantially constant value. 52.The micromirror device of claim 51, wherein the pillar is connected tothe post of the micromirror.
 53. The micromirror device of claim 52,wherein the connect point of the pillar to the post is in the same planeas the hinge.
 54. The micromirror device of claim 52, wherein theconnect point of the pillar to the post is not in the same plane as thehinge.
 55. The micromirror device of claim 53, wherein the connect pointof the pillar to the post is substantially in the middle between thesubstrates.
 56. The micromirror of claim 51, further comprising anotherpost on the first substrate for holding the hinge.
 57. The micromirrorof claim 55, wherein said another post is connected to another pillarthat is placed between the substrates and connected to the secondsubstrate.
 58. The micromirror of claim 56, wherein said another pillarhas a different dimension as the pillar.
 59. The micromirror of claim51, wherein the pillar has a first component that connects the post ofthe micromirror and a second component that is connected to the firstcomponent of the pillar and the second substrate.
 60. The micromirror ofclaim 51, wherein the pillar has a material having acoefficient-of-thermal-expansion that matches that of the post.
 61. Themicromirror of claim 51, wherein the pillar has a material having athermal conductivity that is equal to or higher than that of the post.62. A method of making a spatial light modulator, the method comprising:forming an array of micromirrors on first substrate; providing a secondsubstrate; forming a plurality of pillars on the second substrate;aligning each pillar with one of the micromirrors; and bonding thesubstrates.
 63. The method of claim 62, wherein the step of forming thearray of micromirrors further comprises: depositing a first sacrificiallayer on a first substrate; forming an array of mirror plates on thefirst sacrificial layer; depositing a second sacrificial layer on themirror plates; and forming an array of posts and hinges on the substratesuch that the mirror plate is attached to the hinge, and the hinge isheld on the first substrate by the post.
 64. The method of claim 63,wherein the step of forming the plurality of pillars further comprises:depositing a pillar material on the second substrate; and patterning thedeposited pillar material so as to form the pillars.
 65. The method ofclaim 64, wherein the step of aligning the pillar with the micromirrorfurther comprising: aligning the pillar with the post of the micromirrorsuch that the pillar is connected to the post. 66-70. (canceled)
 71. Aspatial light modulator, comprising: an array of micromirrors on a firstsubstrate; a second substrate; a first sealing material thathermetically bonds the first and second substrates; and a second sealingmaterial other than the first seal material contracting the first andsecond substrate for enhancing the hermetic seal with the first sealingmaterial.
 72. The spatial light modulator of claim 71, wherein the firstsubstrate is glass that is transmissive to visible light.
 73. Thespatial light modulator of claim 71, wherein the first sealing materialis metal.
 74. The spatial light modulator of claim 71, wherein thesecond sealing material is epoxy.
 75. The spatial light modulator ofclaim 71, wherein the first sealing material forms a sealing ringbetween the first and second substrates.
 76. The spatial light modulatorof claim 75, wherein the second sealing material is disposed within thesealing ring.
 77. The spatial light modulator of claim 75, wherein thesecond sealing material is disposed outside the sealing ring.
 78. Thespatial light modulator of claim 71, wherein the second sealing materialis operable to hermetically seal the first and second substrates.
 79. Amicroelectromechanical device, comprising: a first and second substratebonded together; an array of MEMS elements formed on the first substrateand disposed between the substrates; and a plurality of pillars disposedbetween the second substrate and the MEMS elements.
 80. The device ofclaim 79, wherein the pillars are positioned within the MEMS elements.81. The device of claim 79, wherein the pillars positioned within anarea covered by the MEMS elements.
 82. The device of claim 79, whereinthe pillars don't connect the MEMS elements electrically.
 83. The deviceof claim 79, wherein each of the plurality of pillars comprises aninsulating portion.
 84. The device of claim 79, wherein first substrateis light transmissive.
 85. The device of claim 84, wherein the lighttransmissive substrate is glass.
 86. The device of claim 79, wherein thefirst and second substrate is hermetically bonded.
 87. The device ofclaim 79, wherein the pillar is positioned proximate to a reflectivedeflectable element of the MEMS but does not directly connected thereto.88. A method of forming a spatial light modulator for use in a displaysystem, the method comprising: forming a plurality of micromirrors on afirst substrate, wherein each micromirror has a fixed portion and amovable portion; providing a second substrate; and forming a pillar onthe fixed portion of the micromirror and/or on the second substrate. 89.The method of claim 88, wherein the pillar is formed only on the secondsubstrate.
 90. The method of claim 88, wherein the pillar is formed onlyon the fixed portion of the micromirror.
 91. The method of claim 88,wherein the pillar is formed on both of the fixed portion and the secondsubstrate.
 92. The method of claim 88, wherein the pillar is formedwithin an area covered by the micromirrors.
 93. The method of claim 88,wherein the pillar comprises an insulating portion.
 94. The method ofclaim 88, further comprising: bonding the first substrate and the secondsubstrate together to form an assembly such that the micromirrors, theelectrodes and circuitry are positioned between the substrates.
 95. Themethod of claim 94, wherein the step of bonding the first substrate andthe second substrate further comprising: hermetically bonding the firstsubstrate and the second substrate.
 96. The method of claim 95, whereinthe step of hermetically bonding the first substrate and the secondsubstrate further comprising: hermetically bonding the second substrateand the first substrate such that a space between the hermeticallybonded substrate has a pressure lower than 1 atmosphere.
 97. The methodof claim 94, wherein the step of hermetically bonding the firstsubstrate and the second substrate further comprising: bonding thesecond substrate and the first substrate while the micromirrors are notfully surrounded.
 98. The method of claim 88, wherein the step offorming the micromirrors further comprising: forming a plurality ofmirror plates on the first substrate; and forming a plurality of hingeson the light transmissive substrate such that the mirror plates andhinges are located on different planes parallel to the lighttransmissive substrate.